The present invention relates to means for cooling bodies which are exposed to high temperatures. In particular, the present invention relates to means for cooling and transfer of energy in the form of heat away from a body by means of a fluid, such as for instance water. The invention is preferably, but not exclusively, related to a cooling system in which the coolant is permitted to be present simultaneously both in liquid and vapour form.
In the following present invention will be described and discussed in conjunction with means for cooling structural members of and equipment on furnaces for smelting ferro alloys, pig iron and/or carbide. It should be appreciated, however, that the present invention is not limited to such use, but may in general be used wherever the possibility of the appearance of a two-phase condition in the coolant may occur due to excessive heating.
The traditional furnaces for production of ferro alloys, pig iron and carbide require means for cooling those structural members and the equipment which are arranged on or in function on or close to the furnace(s). Cooling of and transfer of energy away from said members or equipment is commonly achieved by means of a liquid coolant, such as for instance water. In recent years, a cooling system is introduced, permitting from a constructional point of view as high external temperature of the members as possible. Instead of depending on the conventional welded, double walled roof structures, relatively thick steel plates with steel pipes for circulating a coolant, the steel pipe(s) being welded on the external side of the roof, is now used. The internal surface temperature of the steel plates in such a structure will be in the order of 150.degree.-400.degree. C. This temperature range is well above the condensation point of water and also well above the condensation point of sulphurous acid, whereby the possibility of corrosion attack due to corrosive moisture is substantially reduced.
A cooling system incorporating steel tubes welded to the roof incorporates, however, certain limitations since the cooling water has a boiling point at 100.degree. C., at atmospheric pressure i.e. well below the internal surface temperature of said steel plates. If the temperature of the body increases so much that the cooling water boils locally the produced steam will block the passage of cooling water through the tube, whereby the possibilities of controlling the temperature is lost. In order to remedy such a undesirable effect it has previously been proposed to use a coolant with a higher boiling point or to apply a high pressure coolant in the system, for example water exposed to high pressure. However, both these remedies incorporate certain vital disadvantages.
If the cooling system is based on a coolant with boiling point higher than 100.degree. C., a heat exchanger must be used in order to reduce the temperature of the coolant before recycling. If on the other hand a high pressure cooling system is used, specific certificates for use and maintenance from the authorities are required, such authorization being dependent upon rigid safety and design requirements. For both systems apply that even small leakage will make the system unsuitable.